$ extempore --run /path/to/file.xtm.
This doesn't get around the 'installing extempore' problem, but once installed it's easy enough for anyone to run an extempore 'program'. You can even hide these 'gruesome details' with a wrapper - shell script, batch file, etc..
Another option is the image/container path. This works well, although you'll be shipping around large (potentially very large) files. Docker is a good option, but you'll still need a relatively savvy end user.
Ultimately, for installation work, generating standalone executables is definitely going to happen - just not sure when.